[vector] #66: ! allocates needlessly

[vector]

#66: ! allocates needlessly
----------------------+-----------------------------------------------------
Reporter:  Khudyakov  |       Owner:     
    Type:  defect     |      Status:  new
Priority:  major      |   Milestone:     
 Version:             |    Keywords:     
----------------------+-----------------------------------------------------
 It looks like ! operator allocates memory each time it's called. Probably
 it creates closure for error function even it's not called. Here is simple
 program which demonstrates issue:

 {{{
 import qualified Data.Vector.Unboxed as U
 import System.Environment

 n :: Int
 n = 137

 vec :: U.Vector Int
 vec = U.enumFromN 1 n

 resSafe :: Int -> Int
 resSafe = U.sum . U.map (\i -> (U.!) vec (i `rem` n)) . U.enumFromN 0

 resUnsafe :: Int -> Int
 resUnsafe = U.sum . U.map (\i -> U.unsafeIndex vec (i `rem` n)) .
 U.enumFromN 0

 main :: IO ()
 main = do
   [t,k] <- getArgs
   case t of
     "safe"   -> print $ resSafe   (read k)
     "unsafe" -> print $ resUnsafe (read k)
 }}}

 Here is allocation statistics:
 {{{
 ./ix safe 100000000 +RTS -s
    3,225,080,440 bytes allocated in the heap
           58,304 bytes copied during GC
           28,816 bytes maximum residency (1 sample(s))
           19,264 bytes maximum slop
                1 MB total memory in use (0 MB lost due to fragmentation)

   Generation 0:  6151 collections,     0 parallel,  0.01s,  0.02s elapsed
   Generation 1:     1 collections,     0 parallel,  0.00s,  0.00s elapsed

   INIT  time    0.00s  (  0.00s elapsed)
   MUT   time    2.90s  (  2.93s elapsed)
   GC    time    0.01s  (  0.02s elapsed)
   EXIT  time    0.00s  (  0.00s elapsed)
   Total time    2.92s  (  2.94s elapsed)

   %GC time       0.5%  (0.6% elapsed)

   Alloc rate    1,110,733,182 bytes per MUT second

   Productivity  99.5% of total user, 98.6% of total elapsed
 }}}

 {{{
 ./ix unsafe 100000000 +RTS -s
           80,624 bytes allocated in the heap
            2,880 bytes copied during GC
           43,784 bytes maximum residency (1 sample(s))
           21,752 bytes maximum slop
                1 MB total memory in use (0 MB lost due to fragmentation)

   Generation 0:     0 collections,     0 parallel,  0.00s,  0.00s elapsed
   Generation 1:     1 collections,     0 parallel,  0.00s,  0.00s elapsed

   INIT  time    0.00s  (  0.00s elapsed)
   MUT   time    1.89s  (  1.89s elapsed)
   GC    time    0.00s  (  0.00s elapsed)
   EXIT  time    0.00s  (  0.00s elapsed)
   Total time    1.89s  (  1.89s elapsed)

   %GC time       0.0%  (0.0% elapsed)

   Alloc rate    42,732 bytes per MUT second

   Productivity 100.0% of total user, 99.8% of total elapsed
 }}}

 Originally discovered by klapaucius https://gist.github.com/1374044

-- 
Ticket URL: <http://trac.haskell.org/vector/ticket/66>
vector <http://trac.haskell.org/vector>
Package vector